Platelet glycoprotein Ibalpha polymorphisms modulate the risk for myocardial infarction

Comparison of the gene encoding, and the predicted amino acid composition of, platelet membrane receptor subunit glycoprotein Ibα in members of the family Felidae

BACKGROUND

There is minimal information regarding platelet receptors in the family Felidae. Comparative studies assist with identifying amino acids critical for protein structure and function.

OBJECTIVE

The purpose of the study was to compare the gene encoding, and the predicted amino acid composition of, platelet membrane receptor subunit GPIbα in Felidae family members.

METHODS

Genomic DNA samples isolated from whole blood of 13 domestic cats and 50 big cats representing 8 different species were subjected to PCR using primers designed to flank the coding region of GPIbα in overlapping fashion. PCR products were separated via electrophoresis on agarose gels, and extracted products were submitted for sequencing. DNA sequences were used to predict the length and amino acid composition of the protein.

RESULTS

Varying protein lengths were predicted in Felidae family members which were primarily due to polymorphisms in the variable number of tandem repeats region encoding the macroglycopeptide region of GPIbα. Other areas of the gene and predicted amino acid compositions were fairly conserved when compared to human sequences and between Felidae family members.

CONCLUSION

Various polymorphisms within GPIbα, including length variants encoding the macroglycopeptide region, were identified in members of the family Felidae. More studies are needed to determine if a correlation exists between various polymorphisms and predisposition for hemorrhage or thrombosis as suggested in people.

Arterial thrombus formation in cardiovascular disease

The pathogenesis of arterial thrombosis is complex and dynamic. Unlike venous thrombi, arterial thrombi typically form under conditions of high blood flow and are mainly composed of platelet aggregates, giving them the appearance of 'white clots'. Strong evidence suggests that arterial thrombi originate as a consequence of an injured atherosclerotic plaque, and that their formation involves the release of prothrombotic material (such as tissue factor), platelet aggregation, and platelet adhesion to the vascular wall. The initially labile platelet plaque is then stabilized by insoluble fibrin produced upon activation of the coagulation cascade. Inherited genetic factors (gene polymorphisms) and acquired predisposing conditions (such as the concentration and activity of clotting factors) can influence both the composition and the size of an arterial thrombus. Further research is needed to elucidate the functions of blood coagulation proteins and cellular elements that are critical to the pathogenesis of arterial thrombosis. This Review explains mechanisms of pathological arterial thrombus formation and discusses genetic and acquired risk factors of atherothrombosis.

Genetic regulation of platelet receptor expression and function: application in clinical practice and drug development

Understanding genetic contributions to platelet function could have profound clinical ramifications for personalizing platelet-directed pharmacotherapy, by providing insight into the risks and possible benefits associated with specific genotypes. This article represents an integrated summary of presentations related to genetic regulation of platelet receptor expression and function given at the Fifth Annual Platelet Colloquium in January 2010. It is supplemented with additional highlights from the literature covering (1) approaches to determining and evidence for the associations of genetic variants with platelet hypo- and hyperresponsive phenotypes, (2) the ramifications of these polymorphisms with regard to clinical responses to antiplatelet therapies, and (3) the role of platelet function/genetic testing in guiding antiplatelet therapy.

High-throughput proteomics detection of novel splice isoforms in human platelets

Alternative splicing (AS) is an intrinsic regulatory mechanism of all metazoans. Recent findings suggest that 100% of multiexonic human genes give rise to splice isoforms. AS can be specific to tissue type, environment or developmentally regulated. Splice variants have also been implicated in various diseases including cancer. Detection of these variants will enhance our understanding of the complexity of the human genome and provide disease-specific and prognostic biomarkers. We adopted a proteomics approach to identify exon skip events - the most common form of AS. We constructed a database harboring the peptide sequences derived from all hypothetical exon skip junctions in the human genome. Searching tandem mass spectrometry (MS/MS) data against the database allows the detection of exon skip events, directly at the protein level. Here we describe the application of this approach to human platelets, including the mRNA-based verification of novel splice isoforms of ITGA2, NPEPPS and FH. This methodology is applicable to all new or existing MS/MS datasets.

Glycoprotein Ibalpha polymorphism T145M, elevated lipoprotein-associated phospholipase A2, and hypertriglyceridemia predict risk for recurrent coronary events in diabetic postinfarction patients

To explore altered platelet function in recurrent coronary event risk among diabetic postinfarction patients, we investigated a function-altering genetic polymorphism (T145M) in the von Willebrand factor binding region of the platelet glycoprotein Ibalpha (GPIbalpha) subunit. The study comprised diabetic and nondiabetic patients of the Thrombogenic Factors and Recurrent Coronary Events postinfarction study. Cox proportional hazards multivariable modeling, adjusted for significant clinical covariates, was performed using the polymorphism and metabolic, inflammatory, and thrombogenic blood markers. Nondiabetic patients demonstrated risk for elevated lipoprotein-associated phospholipase A(2) (Lp-PLA(2)). In contrast, diabetic patients demonstrated significant and independent risk for the M allele of the T145M polymorphism (MT plus MM versus TT, hazard ratio [HR] 3.73, 95% CI 1.90-7.33, P < 0.001), hypertriglyceridemia (2.91, 1.52-5.56, P = 0.001), and elevated Lp-PLA(2) (2.78, 1.45-5.35, P = 0.002). Joint risk (one, two, or three risk factors) expressed as relative outcome rates (compared with no risk factors) were 2.4, 4.0, and 8.2, respectively. We conclude that the M allele of the T145M polymorphism of the GPIbalpha subunit predicts risk for recurrent coronary events in diabetic postinfarction patients, but not in nondiabetic postinfarction patients, supportive of an important role for platelet hyperactivation in diabetic coronary heart disease.

Assessment of Hemostatic Risk Factors in Predicting Arterial Thrombotic Events

Arterial thrombosis results from endovascular injury and, to a lesser extent, alterations in hemostatic equilibrium. Although multiple hereditary and acquired hemostatic risk factors have been described in the pathophysiology of venous thrombosis, the degree and type of abnormalities that contribute to arterial thrombosis are less well understood. Endothelial cell injury with the elaboration of proinflammatory mediators stimulates the process of arterial thrombosis. Although this is most often the result of endovascular injury attributable to atherosclerotic disease, other disease states can elicit a similar response as well. Similarly, once thrombosis has been initiated, variations in the activity of coagulation proteins and endogenous anticoagulants, as well as the kinetics of platelet aggregation, may alter the effectiveness of thrombus formation. Epidemiological studies have identified several acquired or inherited states that may result in endothelial damage or altered hemostatic equilibrium, thereby predisposing patients to arterial thrombosis. These include hyperhomocysteinemia, elevated C-reactive protein, antiphospholipid antibodies, elevated fibrinogen, Factor VII, plasminogen activator inhibitor-1 (PAI-1), hereditary thrombophilias, and platelet hyper-reactivity. This review explores our present understanding of these risk factors in the development of arterial thrombotic events. At present, the literature supports a role for hyperhomocysteinemia, elevated C-reactive protein, and elevated fibrinogen as risk factors for arterial thrombosis. Similarly, the literature suggests that lupus anticoagulants and, to a lesser extent, elevated titers of cardiolipin IgG antibodies predispose to arterial vascular events. In certain subsets of patients, including those with concomitant cardiac risk factors, <55 years of age, and women, hereditary thrombophilias such as carriership of the factor V Leiden and the prothrombin G20210A mutations may confer a higher risk of arterial thrombosis. However, the data on Factor VII, PAI-1, and platelet receptor polymorphisms are contradictory or lacking.